There is a need in the medical field for an inexpensive technique and assembly for injecting uncontaminated medicinal fluid into a patient.
This need exists notwithstanding numerous syringe and filter designs which have been proposed and/or adopted, such as the devices shown in U.S. Pat. Nos. 3,736,932 and 3,817,389.
U.S. Pat. No. 3,817,389 is directed to an improved filter for filtering contamination from medicinal fluid to be injected into a patient. The filter is incorporated in a needle-retaining hub for a hypodermic syringe, whereby the medicinal fluid is filtered to remove contaminants when it is passed through the filter, either when the fluid is drawn from an ampule into the syringe barrel, and/or when the fluid is ejected from the syringe barrel and injected into the patient.
Typically, a two-needle technique is employed in filling the syringe barrel and injecting the patient, whether the filter of the U.S. Pat. No. 3,817,389 type is employed or not. The medicinal fluid is first drawn into the syringe barrel using a first needle, and a second needle is employed for injecting the patient so as to avoid contaminating the medicinal fluid with any foreign matter which may have entered the first needle during filling of the syringe.
U.S. Pat. No. 3,736,932 proposes what might be referred to as a single-needle technique utilizing a needle cannula pointed at both ends and an annular filter having its central opening covered by a diaphragm which is adapted to be pierced by the pointed proximal end of the needle cannula. The needle cannula serves as a filter bypass, whereby the filter will not be loaded with contaminant when the medicinal fluid is drawn into the syringe barrel through the needle (or ejected, depending upon whether the filter is bypassed during aspiration or ejection).
A shortcoming of the invention of the U.S. Pat. No. 3,736,932 patent is the necessity for manually manipulating the double-pointed needle cannula and hub assembly between the step of filling of the syringe and the step of injecting the medicinal fluid into the patient.